This application claims the priority of Hungarian Patent Application No. P9900022 filed Jan. 5, 1999 and Hungarian Patent Application No. P9902483 filed Jul. 22, 1999 which are incorporated herein by reference.
The invention relates to a vehicle tire made of an elastic material, particularly rubber or an elastomer and is provided with a crown portion and two sidewalls connected to the crown portion. Both sidewalls terminate in beads which are clamped to a wheel rim.
Vehicle tires currently in use are generally pneumatic tires, that is, the tires must contain a certain minimum air content under pressure to carry a given load. The air content is defined as the product of the tire volume and the internal pressure. The internal pressure is limited by the strength of the tire structure and the travel comfort.
Pneumatic tires have fared well in practice but are disadvantageous in that they require a very complex structural design to ensure an internal overpressure.
For containment of an internal overpressure the tire body must be reinforced with multi-layer, strength-carrying cord layers, and further, wire hoops made of multi-thread steel wire have to be embedded in the beads.
When the tire is in use, large bending, shearing, pulling and torsion stresses appear between the strength-carrying layers. For this reason such layers have to be provided with rubber layers of different physical characteristics which can resist high-frequency stresses.
Because of the internal overpressure, the vehicle tires must be provided with a special insulating layer to preserve the internal overpressure during use.
To further ensure a containment of the internal overpressure, the beads have to be made of a special material according to a special structural design and cross-sectional configuration to ensure a highly satisfactory seal along the surface which contacts the wheel rim.
A mass production of vehicle tires in accordance with the above-outlined main criteria can be realized only with a series of complicated machine tools which involve a substantial investment and which utilize expensive structural materials and require a costly quality control system.
Various solutions are known particularly for simplifying the manufacturing technology and for producing a more economical product while fully or partially retaining the functional principle of pneumatic tires operating with overpressure.
United Kingdom Patent No. 1,502,808 discloses a structural formation and a manufacturing process of cordless injection-molded pneumatic tires made of an elastomer having a high modulus of elasticity for the purpose of simplifying and rendering less expensive the material structure of pneumatic tires as well as for simplifying the related manufacturing technology.
U.S. Pat. No. 4,230,169 discloses a pneumatic tire which is made of an elastic material without carcass reinforcement and which is provided with a crown portion and sidewalls. Each sidewall terminates in a bead, and the parts between the sidewalls and the crown portion contain an annular thickening or bulge whose strength in the circumferential direction is higher than the strength of adjacent parts, given the fact that the annular thickening or bulge is made of a fibrous material or steel cable.
Load carrying and resilient characteristics of each of the above-mentioned solutions are determined by the overpressure of the air contained within the tire. Such tires are not failure proof, since, if internal air escapes during operation, the tread contour flattens under the load and the vehicle becomes unsteerable. According to an additional drawback of the outlined solutions the tire strength diminishes due to the omission of one part of the cord layers, whereas the overpressure required for ensuring satisfactory load carrying properties and operation cannot be reduced substantially in comparison with conventional vehicle tires. Consequently, tires involving any of the above-outlined solutions have a lower operational safety than traditional tires having embedded cord layers.
Published International Application No. WO 92/12866 discloses a vehicle tire that is made of rubber, preferably of polyurethane elastomer, and has no strength-carrying cord layers, but is provided, under the crown portion, with a belt made of a shock-proof, highly rigid and high-strength material. This solution, while it presents a major milestone by eliminating the disadvantages of previous solutions, has the drawback that the mass manufacture of the sole belt to be mounted under the crown portion is expensive and the substantial mass of the belt results in an appreciable mass increase of the entire vehicle tire.
It is an object of the invention to provide an improved tire which constitutes a further development over the solution disclosed in the International Application No. WO 92/12866 in order to produce a vehicle tire which can be manufactured in a simpler and more economical way, which is characterized by higher lateral stability, lower mass and which is completely puncture-proof.
The invention is based on the recognition that the rolling characteristics and load bearing capacity of the tire as well as the travel comfort on board of the vehicle can be fully ensured without the application of internal overpressure, if the required flexibility of the tire is ensured by suitably positioned springs.
For achieving the proposed solution, the invention provides a tire which is of an elastic material, preferably rubber or an elastomer, and is provided with a crown portion and sidewalls adjacent to the crown portion, wherein both sidewalls terminate in beads by which the tire is mounted on a wheel rim in a pre-stressed (biased) state. In accordance with the invention, the internal surface of the crown portion is supported by arcuately bent leaf springs arranged at specified distances. The individual leaf springs are positioned to connect the two beads with one another and the leaf spring ends are flexibly embedded in the beads. The beads, in turn, are held in a wheel rim in a pre-stressed state.
According to a further advantageous feature of the invention, at least one belt ring having at least one layer is centrally mounted in the crown portion.
According to a further advantageous feature of the invention, a support, which is preferably of flexible material, is centrally positioned on the wheel rim under the leaf springs.
According to a further advantageous feature of the invention, the inner surface of the crown portion is provided with troughs between which stiffening ribs supported by the leaf springs are situated.
According to a further advantageous feature of the invention, the central line of the stiffening ribs situated between the troughs forms an angle xcex1=90xc2x0 with the crown portion line in the symmetry plane of the tire and, proceeding towards to sidewalls, the angle xcex1 diminishes to an angle xcex11, wherein
60xc2x0 less than xcex11 less than xcex1=90xc2x0.
According to a further advantageous feature of the invention, the stiffening ribs are situated in the vehicle tire at uniform distances from each other and are disposed such that a plane containing the center of gravity of the vehicle tire and the central line of the respective stiffening rib, forms, in the case of each stiffening rib, an identical angle xcex2 with the symmetry plane perpendicular to the rotary axis of the vehicle tire, wherein
60xc2x0 less than xcex2 less than 120xc2x0.
According to a further advantageous feature of the invention stiffening cross ribs are provided which interconnect the stiffening ribs.
According to a further advantageous feature of the invention the beads are provided with troughs which are spaced at specified distances from each other and which clamp the edge of the wheel rim horn.
According to a further advantageous feature of the invention, the sidewalls are provided with protective beads externally covering the wheel rim horns.
According to a further advantageous feature of the invention the leaf springs have thickened, arcuate ends, and the beads have slots which receive the arcuate ends and have arcuate surfaces abutting the arcuate ends of the leaf springs.
According to a further advantageous feature of the invention at least one reinforcement ring is embedded in the sidewalls of the vehicle tire.